This January, 25-year-old Josh Johannessen was planning to quit his serving job at Red Robin in Rockaway, NJ, to hop on a cross-country bike journey to Seattle. He had saved up $3,000 to visit ballparks throughout the country — but he wanted it to be more than cycling and Cracker Jacks.

“I had this urge to just explore and get out of town,” Johannessen, who lives with his parents in Budd Lake, NJ, tells The Post. “But I was also inspired by stories about bikers raising money for charity, and I wanted to feel like I was riding with a purpose.”

So when, two weeks later, he saw on Facebook that his former co-worker Robin Reed, 42, had been diagnosed with breast cancer, he decided to dedicate his journey to her and launched a GoFundMe page to raise money to cover Reed’s medical treatments.

“I had this sinking feeling in my stomach that this is happening to one of the nicest people in the world,” Johannessen explains. “I wanted to do something about it.”

So far, his page has raised nearly $12,000 of his $25,000 goal — and on Wednesday morning, he began his quest West with the hope of helping his friend in need.

“When Josh told me about his fund-raising, I was in tears,” Reed, from Byram, NJ, tells The Post. “He truly is my guardian angel.”

Johannessen and Reed met in 2009 when they were both servers at an Applebee’s in Flanders, NJ. She worked the weekend shift on top of her weekday job as a pre-K teacher. Reed encouraged Johannessen to finish his bachelor’s degree at Montclair State University, while Johannessen would offer to baby-sit Reed’s daughters, Chloe, 14, and Mackenzie, 8.

They fell out of touch in early 2015 when Johannessen took a new job at Red Robin. In October, Reed was diagnosed with ductal carcinoma breast cancer.

She had to quit her serving job and temporarily leave her teaching position to undergo chemotherapy. Her husband John’s salary and her short-term disability checks are not enough to support their family. Between her chemotherapy and her upcoming double mastectomy, Reed says treatments could cost her up to $21,000.

Johannessen set off on his journey Wednesday morning from Seaside Heights, NJ, and plans to pedal to 12 baseball stadiums across the country before ending his journey in Seattle on Aug. 24. He created a profile on Couchsurfing.com to crash at strangers’ apartments for free at night, and he even packed a tent.

“I was in tears saying goodbye to him,” says Reed, who was there to see him off. “I knew he always wanted to do a trip like this, but I was overwhelmed with gratitude when he told me he was also doing this for me.”